1. Field of the Invention
This invention relates to a dip-coating method and apparatus for forming a flat smooth coated film surface on the surface of an article.
More particularly the present invention is to provide a method and apparatus for obtaining a very fine coated film having no irregularity on an article to be coated by making ultrasonic waves act on a coating solution and forming a uniform surface liquid flow in a coating solution tank. In case the present invention is applied to coat the surface of such optical product as a mirror or lens, a remarkable effect that a product quality of such excellent level as has never been realized before will be obtained.
2. Description of Prior Arts
A method of forming a coated film on the surface of an article to be coated by dipping the article in a coating solution and then pulling the article up out of the coating solution at a low speed has been already utilized as a dip-coating method. This method has demerits that the article to be coated is limited to be of a simple shape having no solution pool but has merits that the obtained coating film is high in the smoothness and that the entire surface of the article to be coated can be coated at once, and thus is used for such surface coating as the under coating or upper coating of a metal or synthetic resin article.
In case the coated article is to be used for such optical product as a mirror, lens or glazing or in case it is to be printed or plated as a secondary work, a higher smoothness of the coating film having no irregularity will be required.
These irregularity defects are called "pinholes", "blemishes", "splashes" and "craters" in the industry. Their elimination is made an important problem of securing the quality.
These defects of the coated film can be comparatively reduced by such methods wherein the article to be coated is washed and cleaned with a detergent or the like in advance, such impurities as dust in the coating solution are filtered off to be removed and further the entire atmosphere in which the article is dip-coated and the coated film is dried to be hardened is cleaned. But the smoothness of the coated film has been insufficient.
Further, there is an attempt to secure the smoothness of the coated film by flowing the coating solution in the coating tank so quietly as to spout. However, it has not been satisfactory.